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What Are Kidney Stones?

A kidney stone forms when compounds in the urine bind together and crystalize into a hard mass. Most people do not realize they have a stone until it moves from the kidney into the ureter and blocks the flow of urine from that kidney. This causes severe pain and often results in an emergency room visit.

Types of kidney stones

There are four common stone types:

  • Calcium stones: The majority of kidney stones are composed of calcium oxalate, which results from high concentrations of oxalic acid in the urine. This is caused by a combination of diet, lifestyle and genetics. Less commonly, calcium phosphate stones occur due to high alkaline content in the urine.
  • Uric acid stones: These stones are associated with having acidic urine. Risk factors for this type of stone include obesity, bowel conditions, diabetes, gout and a diet that is high in animal protein and low in fruits and vegetables.
  • Struvite/infection stones: These stones form in patients with chronic urinary tract infections (UTIs).
  • Cystine stones: These relatively rare stones form in people who lack the ability to process cystine, one of many amino acid building blocks for protein formation. Cystine stones typically first appear in childhood or in young adulthood.

Symptoms of kidney stones

Most kidney stones do not cause any symptoms and often go undiagnosed. However, sometimes when stones start to pass from a kidney, they can block the outflow of urine, resulting in pain in the back.

Other symptoms may include:

  • A sharp, cramping pain on the left or right side of the back that often travels downward to the lower abdomen or groin
  • Frequent urination with discomfort
  • Fever
  • Blood in the urine
  • Nausea and vomiting
What causes kidney stones? ›
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